A promising new technique for efficient enrichment of an isotopic mixture, such as U.sub.235 enrichment of uranium, involves exposing a vapor of the mixture to carefully chosen bandwidths of laser radiation for selectively photoionizing the desired isotope. Ions of the desired isotope are then separated from the neutral particles by the application of strong electric and/or magnetic fields in accordance with magnetohydrodynamic techniques.
Apparatus for effecting such separation typically comprises a source for emitting neutral particles of the isotopic mixture in a generally defined direction, and a plurality of spaced apart ion separation electrodes having relatively large area surfaces oriented generally parallel to the direction of neutral particle emission and elongated surfaces of relatively narrow width substantially perpendicular to such direction. The latter surfaces can be referred to as the leading edges of the electrodes.
As neutral particles pass through ionization regions between spaced apart electrode pairs, they are subjected to isotopically selective photoionizing radiation from carefully tuned lasers. Ions of the selected isotope are separated from neutral particles in the resulting plasma by simultaneously applying a voltage differential between the electrodes and magnetic field perpendicular to the electrical field. The positive ions of the selected isotope collect on the negative electrodes for removal and further processing while the neutral particles deposit onto a "tailings" plate downstream.
One difficulty in the operation of such apparatus arises because the photoionizing radiation, for a variety of practical reasons, does not fill the entire space between the electrodes. Consequently the neutral vapor passing through the unexposed space mixes with the exposed but unionized vapor (depleted vapor) at a "tailings" plate. Such mixture represents a loss in enrichment as the unexposed neutral vapor will have a greater enrichment than the exposed depleted vapor.
In addition, there is a tendency for the leading edges of the ion separation electrodes to collect large deposits of the neutral particle vapor. Such deposits reduce the level of enrichment of material collected on the negative electrodes and require periodic cleaning of the positive electrodes.